1791

January–March

• January 2 – Big Bottom massacre in the Ohio Country, marking the beginning of the Northwest Indian War.
• January 12 – Holy Roman troops reenter Liège, heralding the end of the Liège Revolution, and the restoration of its Prince-Bishops.
• January 25 – The British Parliament passes the Constitutional Act 1791, splitting the old province of Quebec into Upper and Lower Canada.
• February 8 – The Bank of the United States, based in Philadelphia, is incorporated by the federal government with a 20-year charter and started with $10,000,000 capital. ^[1]
• February 21 – The United States opens diplomatic relations with Portugal.
• March 2 – French Revolution:
  • The abolition of guilds is enacted.
  • A mechanical semaphore line for rapid long-distance communication is demonstrated by Claude Chappe in Paris.
• March 4 – Vermont is admitted, as the 14th U.S. state.
• March 13 – Thomas Paine's chief work Rights of Man (first part) is published in London.^[2]
• March – French Revolution: In France, the National Constituent Assembly accepts the recommendation of its Commission of Weights and Measures, that the nation should adopt the metric system.

April–June

• April 21 – The first of forty boundary stones, delineating the borders of the new District of Columbia in the United States, is laid at Jones Point Light, in Alexandria, Virginia.
• May 3 – The Sejm of the Polish–Lithuanian Commonwealth proclaims the Constitution of May 3, 1791, the first modern codified constitution in Europe.
• June 20 – French Revolution – Flight to Varennes: The French Royal Family is captured when they try to flee in disguise.
• June 21 – The Ordnance Survey is founded in Great Britain.^[3]

July–September

Date	Events	Photos
Wednesday, July 8	Composer Joseph Haydn is awarded an honorary doctorate of music at the University of Oxford.
Wednesday, July 11	The ashes of Voltaire are transferred to the Panthéon.
Sunday, July 14	The Priestley Riots against Dissenters break out in Birmingham, England.
Sunday, July 17	French Revolution: The Champ de Mars Massacre occurs.
Sunday, August 4	The Treaty of Sistova is signed, ending the Ottoman–Habsburg wars.
Sunday, August 6	The Brandenburg Gate in Berlin is finished.
Sunday, August 7	George Hammond is appointed as Great Britain's first minister to the United States. [1]
Sunday, August 21	Haitian Revolution: A slave rebellion breaks out in the French colony of Saint-Domingue.
Sunday, August 26	John Fitch is granted a patent for the steamboat in the United States.
Sunday, August 27	Declaration of Pillnitz - A proclamation by Frederick William II of Prussia and Habsburg Holy Roman Emperor Leopold II, affirms their wish to "put the King of France in a state to strengthen the bases of monarchic government."
Sunday, September 6	Wolfgang Amadeus Mozart's opera seria, La clemenza di Tito, premières at the Estates Theatre in Prague to mark the coronation of Leopold II as King of Bohemia.
Sunday, September 9	The capital of the United States, Washington, D.C., is named after President George Washington.
Sunday, September 13	French Revolution: Louis XVI of France accepts the final version of the completed constitution.
Sunday, September 14	French Revolution: The Papal States lose Avignon to Revolutionary France.
Sunday, September 25	Mission Santa Cruz is founded by Father Fermín Lasuén, becoming the 12th mission in the California mission chain.
Sunday, September 28	French Revolution: The law on Jewish emancipation is promulgated in France, the first such legislation in modern Europe.
Sunday, September 30	Wolfgang Amadeus Mozart's singspiel opera The Magic Flute (Die Zauberflöte) premières at the Freihaus-Theater auf der Wieden in Vienna.

October–December

• October – French Revolution: The Legislative Assembly (France) convenes.
• October 9 – Mission Nuestra Señora de la Soledad is founded by Father Fermín Lasuén, becoming the 13th mission in the California mission chain.
• October 28 – French Revolution: The Declaration of the Rights of Woman and the Female Citizen is published in France.
• November 4 – St. Clair's Defeat, the worst loss suffered by the United States Army in fighting against American Indians, takes place in what is now Mercer County, Ohio. Miami fighters led by Chief Mihsihkinaahkwa (Little Turtle) and by Shawnee warriors commanded by War Chief Weyapiersenwah (Blue Jacket) rout the forces of General Arthur St. Clair and kill 630 U.S. soldiers, along with hundreds of civilians. ^[4]
• December 4 – The first issue of The Observer, the world's first Sunday newspaper, is published in London.
• December 5 – Austrian composer Wolfgang Amadeus Mozart dies aged 35 at his home in Vienna, perhaps of acute rheumatic fever, and is buried two days later.
• December 15 – Ratification by the states of the first ten amendments to the United States Constitution is completed, creating the United States Bill of Rights. Two additional amendments remain pending, and one of these is finally ratified in 1992, becoming the Twenty-seventh Amendment.
• December 23 – Pale of Settlement established by ukase of Catherine the Great, specifying those areas of the Russian Empire in which Jews are permitted permanent residency.

Date unknown

• The first American ship reaches Japan.
• An ordinance is written barring the game of baseball within 80 yards of the Meeting House in Pittsfield, Massachusetts (first known reference to the game of baseball in North America).
• The first serious secondary education school open to girls in Denmark, the Døtreskolen af 1791, is founded in Copenhagen.
• The School for the Indigent Blind, the oldest continuously operating specialist school of its kind in the world, is founded in Liverpool, England, by blind ex-merchant seaman, writer and abolitionist Edward Rushton.
• The Casbah of Algiers Palace is completed.^[5]

Date Unknown

• Enriqueta Favez, Swiss physician, surgeon (d. 1856)